<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>p1</title>
    <style>
        div{
            width: 100px;
            height: 100px;
            background-color: red;
        }
        #ddd{
            font-size: 50px;
            border: 5px solid blue;
            border-radius: 15px;
            box-shadow: 5px 5px 5px 5px #000;
            background-image: linear-gradient( 30deg,purple,blue,pink);
        }
        .bt{
            background-color: yellow;
        }
        #d2:hover{
            background-color: green;
        }
    </style>
</head>
<body>
    <div style="color: blue;">1</div>
    <div id="d2">2</div>
    <div id="ddd">3</div>
    <hr>
    <h3 class="bt">标题1</h3>
    <h3 class="bt">标题2</h3>
    <h3>标题3</h3>
    <h3>标题4</h3>
</body>
</html>